An awareness of what is going on with your exhaust system can keep your engine running at peak performance and avoid costly repairs.
By Capt. Ken Kreisler
Years back, a friend of mine, short a mate for a late afternoon, early evening six-pack charter, asked me to work the deck for him. Fishing was good and on the way back to the barn, with just a few minutes to his dock, I noticed we were riding a bit low in the water and that the bilge pumps were now discharging fairly regularly. I told him about it and decided we would check things out as soon as we shut down and our fishermen were on their way.
We discovered there was quite a bit of water below as well as having collected forward. I asked him to hit the starter button and as the engine turned over, I was shocked to see raw water pouring out from underneath the hose connecting to the riser. Instead of being discharged out the exhaust pipe, it was bucketing into the boat. When we took things apart, we discovered the riser itself was totally corroded from the inside with very little material left being held by the hose clamps. We had dodged a very big bullet and one that neither of us would ever forget.
Just like any other critical part of your boat’s engine, the exhaust system needs proper attention to ensure safe and smooth operation. Besides the chance of being exposed to noxious fumes, not doing so can lead to severe engine problems and yes, even sinking.
We usually take the exhaust system for granted and expect there is little if anything that can go wrong. First mistake. This is a very important maintenance component and while you should call in the experts if you suspect there is a problem brewing, there are some things you can look for to help you head off the sticker shock of a major engine overhaul.
By now, we all know that when an up stroking cylinder compresses atomized diesel fuel—or when a spark goes off in a gasoline engine—there is detonation. Once that occurs, the resultant gases given off need somewhere to go. And it is during the exhaust phase of your engine’s operation that this is accomplished. Not being able to efficiently do so will result in back pressure problems, the first of many that can occur.
“Most people don’t worry about it until something goes wrong; and when it does, it can be pretty bad,” says Jorge Lang, Operations Manager at Ft. Lauderdale’s DeAngelo Exhaust Systems. “Think of it as a human being; it has to inhale, through the air intakes, and exhale through the exhaust.”
Basically, back pressure is the inability for your engine to breathe properly and as easily as it should and results in poor performance, a cut in fuel economy, and decreased speed. In addition, there can be consequential damage to internal engine parts such as valves, stems, injectors, and critical gaskets. “If the exhaust is running straight out, you have no back pressure. But if it has to go through a ninety degree turn or through a muffler, or you’re going to throw water into that gas flow, you’re adding resistance.”
Given the fact that diesel engine manufactures do not supply exhaust risers with their engines, this critical piece of equipment is therefore, an after market component where improper system design and sizing, that being the diameter of the exhaust pipe, can worsen the problem. “If the material used is also not of the proper grade, what you wind up with is a lethal combination of metal, exhaust fumes, and salt water that does not get along very well,” said Lang. “We’ve seen it all; some even thinking a Home Depot pipe job will suffice.”
Poorly designed exhausts can also allow water to flow back into the exhaust manifold, especially during large following sea conditions, and make its way into the engine. “There are a number of factors that determine how long a riser will last. Some of these include the quality of the welds, materials used, if the riser holds water when the engine is shut down, and how well it is supported.” Lang also suggests a regular inspection underneath your engine bed and stringers to look for rust spots, indicating a possible leak coming from somewhere.
Just as with your other important engine parameters, it’s best to have a base line for your exhaust system including correct operating temps for both cooling and exhaust systems, the right amount of visible exhaust flow should you not have an under water system, and of course, taking regular back pressure readings from your engine monitoring data. OEM’s have different predetermined back pressure limits based on critical internal features, so it’s best to check your engine manual or have the discussion with your engine manufacturer. Remember, the higher the back pressure, the more restricted the exhaust system will be. “Exceeding those limits will lead to problems,” said Lang.
But what if your running bottom and props are not fouled and your back pressure is within
acceptable limits? “This happens a lot, especially with boats up north that are stored for the winter,” says Mechanical Engineer and Manager of Centek Industries’ Product Design & Engineering Bert Browning. “Something may have made its winter home in the exhaust pipe and either died or made a nest or some other kind of living space.” A careful check for obstructions before getting your boat back in the water should be part of your regular preventive maintenance regimen.
“While back pressure issues can result in higher exhaust temps you don’t necessarily need to have back pressure problems for this to result,” offered Browning. You can have some cooling water issues as a result of a faulty water raw pump or failed impellers. These should also be checked regularly. If that impeller is degraded or damaged, not only will the proper amount of cooling water be diminished but, should any of the vanes break loose, the rubber material can be pushed all the way through the cooling system and severely clog the water flow. Or, you may have picked up a plastic bag or some other debris through the intake hose. In this case, make sure you shut off—and open once done—the seacock before attempting to have a look. And always make sure, just as you check your oil and fluid levels before starting up, to have a look at your raw water strainer and clean the basket if any debris or fouling is present.
Another area to check is the condition of the blue and black hoses and the clamps, especially those connected to the riser and the mixing elbow. With high temperature ratings, blue hose, rated at 350F if preferable. Any telltale problems will show up as a discoloration on some portion of the hose, usually at the clamp site. And it’s a given that hoses should be double clamped. Other revealing signs, such as those with fiberglass, gelcoated, or even Awlgripped systems, will be a yellowish-brown discoloration and ‘flaky’ deterioration. “With fiberglass, over time, the resin will ‘cook out’ and start weeping resulting in salt deposits forming on the exterior surface of the exhaust pipe,” said Browning. “Losing the resin will cause the pipe to eventually soften and compress under the clamp force.”
Keeping tabs on your exhaust system is as important as any other aboard your boat. Check with your yard manager during yearly haul out time and have the risers inspected as part of your maintenance regimen. Besides the fact that exhaust fumes are noxious and can cause health problems, your engine will not be running as efficiently as it was designed to do and, allowed to continue operating under diminished conditions, will lead to costly repairs.
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